With the diminishing supply of crude mineral oil, use of renewable energy sources is becoming increasingly important for the production of liquid fuels. These fuels from renewable energy sources are often referred to as biofuels.
Biofuels derived from non-edible renewable energy sources, such as cellulosic materials, are preferred as these do not compete with food production. These biofuels are also referred to as second generation, renewable or advanced, biofuels. Most non-edible renewable energy sources, however, are solid materials that are cumbersome to convert into liquid fuels.
For example, the process described in WO 2010/062611 for converting solid biomass to hydrocarbons requires three catalytic conversion steps. First the solid biomass is contacted with a catalyst in a first riser operated at a temperature in the range of from about 50 to about 200° C. to produce a first biomass-catalyst mixture and a first product comprising hydrocarbons (referred to as pretreatment). Hereafter the first biomass-catalyst mixture is charged to a second riser operated at a temperature in the range of from about 200° to about 400° C. to thereby produce a second biomass-catalyst mixture and a second product comprising hydrocarbons (referred to as deoxygenating and cracking); and finally the second biomass-catalyst mixture is charged to a third riser operated at a temperature greater than about 450° C. to thereby produce a spent catalyst and a third product comprising hydrocarbons. The last step is referred to as conversion to produce the fuel or specialty chemical product. WO 2010/062611 mentions the possibility of preparing the biomass for co-processing in conventional petroleum refinery units. The process of WO 2010/062611, however, is cumbersome in that three steps are needed, each step requiring its own specific catalyst.
WO2010/135734 describes a method for co-processing a biomass feedstock and a refinery feedstock in a refinery unit comprising catalytically cracking the biomass feedstock and the refinery feedstock in a refinery unit comprising a fluidized reactor, wherein hydrogen is transferred from the refinery feedstock to carbon and oxygen of the biomass feedstock. In one of the embodiments WO2010/135734 the biomass feedstock comprises a plurality of solid biomass particles having an average size between 50 and 1000 microns. In passing, it is further mentioned that solid biomass particles can be pre-processed to increase brittleness, susceptibility to catalytic conversion (e.g. by roasting, toasting, and/or torrefication) and/or susceptibility to mixing with a petrochemical feedstock.
In the article titled “Biomass pyrolysis in a circulating fluid bed reactor for production of fuels and chemicals” by A. A. Lappas et al, published in Fuel, vol. 81 (2002), pages 2087-2095, an approach for biomass flash pyrolysis in a circulating fluid bed (CFB) reactor is described. The CFB reactor comprised a vertical riser type reactor (7.08 mm ID). The riser height was 165 cm. An integrated screw feeder system was designed and constructed for effective biomass introduction into the unit. From the screw feeder the biomass was introduced at the bottom of the riser, using a specifically designed injection-mixing system. This system consisted of a large diameter bottom vessel connected through a conical section with the riser reactor. In all experiments lignocell HBS 150-500 supplied by Rettenmaier GmbH (particle size 200-400 micrometer) was used as biomass feedstock. In the conventional biomass pyrolysis tests silica sand was used as a heat carrier. Catalytic biomass pyrolysis was performed using a commercial equilibrium FCC catalyst supplied by a Greek refinery. The Biomass pyrolysis experiments were performed at riser temperatures in the range of 400-500° C. Each biomass pyrolysis run required 2 hour for the line out and the heating up of the unit and 3 hours of a steady state operation.
It would be an advancement in the art to improve the above processes further.
For example, it has now for the first time been recognized that due to residual moisture in a solid biomass feedstock, such solid biomass feedstock may cause additional gasses to be formed during catalytic cracking thereof. These additional gases may cause a solid biomass feedstock to expand more in a riser reactor than a conventional petroleum based feedstock. The additional gas formation may lead to an increased gas velocity and/or an increased pressure. An increased gas velocity may in turn lead to insufficient conversion of the solid biomass feedstock and/or insufficient robustness of the process. Higher pressures may lead to increased safety risks.
In addition unconverted solid biomass particles may cause erosion and/or abrasion of the hardware. Further unconverted solid biomass material particles may increase the fouling in a reactor. This in turn may effect the robustness and reliability of the process.
Hence, in order to scale up the catalytic cracking of the solid biomass feedstock to a commercial scale, the process may require improvements to meet nowadays conversion, robustness, maintenance and/or safety requirements.